Associations between age at first calving and lactation performance of Holstein cows in selected Iranian herds

Abstract

Introduction: The aim of this study was to investigate the relationship between age at first calving with milk production and its composition in Holstein dairy herds.
Materials & Methods: Recorded data from nine Holstein flocks including 38702 head from 2002 to 2020, which were collected by the Iranian Animal Breeding Center, were used for analysis. The relationship between age at first calving with milk production milk composition was determined by regression analysis and the correlation between these traits were investigated.
Result: Age at first calving had a significant effect on all studied traits including milk production, milk fat and protein yield. The correlation between milk production, milk fat and protein yield with age at first calving was -0.61390, -0.0190906 and -0.07018, respectively. The results show that the age at first calving less than 21 months has a negative effect on milk production, mild fat and protein content and with increasing age at first calving from 21 to 23 months increases milk production and fat and protein yield and from 25 months to 38 fat and protein yield decreased irregularly trend.
Conclusion: According to the results, the optimal age at first calving is 22 months (21 to 23 months) and it seems that reducing it to 22 months in herds can be an effective management method in reducing costs and increasing milk production.